Carrier proteins are used to improve the immune response to polysaccharide immunogens. Such carrier proteins can be particularly advantageous in the induction of an immune response in the very young and are therefore found in a number of pediatric vaccines. The recommended pediatric immunization schedule includes a significant number of vaccines including hepatitis B vaccine at birth; starting at six weeks, all of diphtheria/tetanus/pertussis (DTaP), rotavirus, H. influenzae type b (Hib) conjugate, inactivated poliovirus and pneumococcal conjugates; starting at six months, inactivated influenza vaccines; starting at 12 months, measles/mumps/rubella (MMR), varicella, and hepatitis A; and after two years, meningococcal conjugate. Among this list, the following are polysaccharide conjugates: Hib conjugate (e.g., HbOC—a diphtheria CRM197 conjugate); pneumococcal conjugates (e.g., Prevnar—a diphtheria CRM197 conjugate and Synflorix—a protein carrier derived from non-typeable Haemophilus influenzae strains); and meningococcal conjugate (e.g., Menactra—a diphtheria CRM197 conjugate).
Adding new vaccines to the current pediatric immunization schedule can encounter two potential problems that must be addressed. First, the issue of carrier-induced epitopic suppression (or “carrier suppression”, as it is generally known) must be addressed, particularly suppression arising from carrier priming. “Carrier suppression” is the phenomenon whereby pre-immunization of an animal with a carrier protein prevents it from later eliciting an immune response against a new antigenic epitope that is presented on that carrier (Herzenberg et al. (1980) Nature 285: 664-667).
As reported in Schutze et al. (1985) J Immunol 135:2319-2322, where several vaccine antigens contain the same protein component (being used as an immunogen and/or as a carrier protein in a conjugate) then there is the potential for interference between those antigens. Schutze et al. observed that the immune response against an antigen that was conjugated to a tetanus toxoid (Tt) carrier was suppressed by pre-existing immunity against Tt.
Dagan et al. observed that a combination of DTP vaccines with a Hib conjugate vaccine was adversely affected where the carrier for the Hib conjugate was the same as the tetanus antigen from the DTP vaccine ((1998) Infect Immun 66:2093-2098). Dagan et al. concluded that this “carrier suppression” phenomenon, arising from interference by a common protein carrier, should be taken into account when introducing vaccines that include multiple conjugates.
In contrast to Schutze et al. and Dagan et al., Barington et al. reported that priming with tetanus toxoid had no negative impact on the immune response against a subsequently-administered Hib-Tt conjugate, but suppression was seen in patients with maternally acquired anti-Tt antibodies ((1994) Infect Immun 62:9-14). Di John et al., however, observed an “epitopic suppression” effect for a Tt-based peptide conjugate in patients having existing anti-Tt antibodies resulting from tetanus vaccination ((1989) Lancet 2(8677):1415-8).
Granoff et al. suggested that a conjugate having CRM197 (a detoxified mutant of diphtheria toxin) as the carrier may be ineffective in children that had not previously received diphtheria toxin as part of a vaccine (e.g., as part of a DTP or DT vaccine) ((1993) Vaccine Suppl 1: 546-51). This work was further developed in Granoff et al. (1994) JAMA 272:1116-1121, where a carrier priming effect by D-T immunization was seen to persist for subsequent immunization with Hib conjugates.
In Barington et al. (1993) Infect Immun 61:432-438, the authors found that pre-immunization with a diphtheria or tetanus toxoid carrier protein reduced the increase in anti-Hib antibody levels after a subsequent immunization with the Hib capsular saccharide conjugated to those carriers, with IgG1 and IgG2 being equally affected. Responses to the carrier portions of the conjugates were also suppressed. Furthermore, a more general non-epitope-specific suppression was seen, as pre-immunization with one conjugate was seen to affect immune responses against both the carrier and saccharide portions of a second conjugate that was administered four weeks later.
Thus, given the confusion over the impact of “carrier suppression,” having additional carrier proteins available for conjugation will be beneficial to reduce such adverse interactions.
Second, given the already crowded immunization schedule, addition of new vaccines to the immunization schedule will become increasingly difficult due to possible adverse interactions, but also due simply to the number of separate injections required. Thus, being able to combine vaccines into a single injection such as the DTaP or MMR vaccines is advantageous. Having additional carrier proteins that can enhance an immune response to a polysaccharide immunogen as well as induce an immune response to itself will be beneficial as it can allow combination of vaccines against different pathogens into a single injectable composition.
It is an object of the invention to provide further and/or better carrier polypeptides for conjugation to polysaccharide immunogens. It is also an object of the invention to provide carrier polypeptides for conjugation to polysaccharide immunogens where the carrier polypeptides can be used in immunization against pathogenic E. coli strains, and more particularly against intestinal pathotypes (e.g. EAEC, EIEC, EPEC and ETEC strains) as well as ExPEC pathotypes. It is also an object of the invention to provide conjugates with such further and/or better carrier polypeptides where the polysaccharide immunogen is a glucan polysaccharide, which in some embodiments can be used in immunization against fungal pathogens.